1. Field of the Invention
This invention relates to the field of oilfield equipment, and in particular to a system and method for conversion between conventional hydrostatic pressure drilling to managed pressure drilling or underbalanced drilling using a rotating control device.
2. Description of the Related Art
Marine risers are used when drilling from a floating rig or vessel to circulate drilling fluid back to a drilling structure or rig through the annular space between the drill string and the internal diameter of the riser. Typically a subsea blowout prevention (BOP) stack is positioned between the wellhead at the sea floor and the bottom of the riser. Occasionally a surface BOP stack is deployed atop the riser instead of a subsea BOP stack below the marine riser. The riser must be large enough in internal diameter to accommodate the largest drill string that will be used in drilling a borehole. For example, risers with internal diameters of 21¼ inches have been used, although other diameters can be used. A 21¼ inch marine riser is typically capable of 500 psi pressure containment. Smaller size risers may have greater pressure containment capability. An example of a marine riser and some of the associated drilling components, such as shown in FIGS. 1 and 2, is proposed in U.S. Pat. No. 4,626,135.
The marine riser is not used as a pressurized containment vessel during conventional drilling operations. Drilling fluid and cuttings returns at the surface are open-to-atmosphere under the rig floor with gravity flow away to shale shakers and other mud handling equipment on the floating vessel. Pressures contained by the riser are hydrostatic pressure generated by the density of the drilling fluid or mud held in the riser and pressure developed by pumping of the fluid to the borehole. Although operating companies may have different internal criteria for determining safe and economic drill-ability of prospects in their lease portfolio, few would disagree that a growing percentage are considered economically undrillable with conventional techniques. In fact, the U.S. Department of the Interior has concluded that between 25% and 33% of all remaining undeveloped reservoirs are not drillable by using conventional overbalanced drilling methods, caused in large part by the increased likelihood of well control problems such as differential sticking, lost circulation, kicks, and blowouts.
In typical conventional drilling with a floating drilling rig, a riser telescoping or slip joint, usually positioned between the riser and the floating drilling rig, compensates for vertical movement of the drilling rig. Because the slip joint is atop the riser and open-to-atmosphere, the pressure containment requirement is typically only that of the hydrostatic head of the drilling fluid contained within the riser. Inflatable seals between each section of the slip joint govern its pressure containment capability. The slip joint is typically the weakest link of the marine riser system in this respect. The only way to increase the slip joint's pressure containment capability would be to render it inactive by collapsing the slip joint inner barrel(s) into its outer barrel(s), locking the barrels in place and pressurizing the seals. However, this eliminates its ability to compensate for the relative movement between the marine riser and the floating rig. Such riser slips joints are expensive to purchase, and expensive to maintain and repair as the seals often have to be replaced.
Pore pressure depletion, the hydraulics associated with drilling in deeper water, and increasing drilling costs indicate that the amount of known resources considered economically undrillable with conventional techniques will continue to increase. New and improved techniques, such as underbalanced drilling (UBD) and managed pressure drilling (MPD), have been used successfully throughout the world in certain offshore drilling environments. Both technologies are enabled by drilling with a closed and pressurizable circulating fluid system as compared to a drilling system that is open-to-atmosphere at the surface. Managed pressure drilling (MPD) has recently been approved for use in the Gulf of Mexico by the U.S. Department of the Interior, Minerals Management Service, Gulf of Mexico Region. Managed pressure drilling is an adaptive drilling process used to more precisely control the annular pressure profile throughout the wellbore. MPD addresses the drill-ability of a prospect, typically by being able to adjust the equivalent mud weight with the intent of staying within a “drilling window” to a deeper depth and reducing drilling non-productive time in the process. The drilling window changes with depth and is typically described as the equivalent mud weight required to drill between the formation pressure and the pressure at which an underground blowout or loss of circulation would occur. The equivalent weight of the mud and cuttings in the annulus is controlled with fewer interruptions to drilling progress while being kept above the formation pressure at all times. An influx of formation fluids is not invited to flow to the surface while drilling. Underbalanced drilling (UBD) is drilling with the hydrostatic head of the drilling fluid intentionally designed to be lower than the pressure of the formations being drilled, typically to improve the well's productivity upon completion by avoiding invasive mud and cuttings damage while drilling. An influx of formation fluids is therefore invited to flow to the surface while drilling. The hydrostatic head of the fluid may naturally be less than the formation pressure, or it can be induced.
These techniques present a need for pressure management devices when drilling with jointed pipe, such as rotating control heads or devices (referred to as RCDs). RCDs, such as disclosed in U.S. Pat. No. 5,662,181, have provided a dependable seal between a rotating tubular and the marine riser for purposes of controlling the pressure or fluid flow to the surface while drilling operations are conducted. Typically, an inner portion or member of the RCD is designed to seal around a rotating tubular and rotate with the tubular by use of an internal sealing element(s) and bearings. Additionally, the inner portion of the RCD permits the tubular to move axially and slidably through the RCD. The term “tubular” as used herein means all forms of drill pipe, tubing, casing, drill collars, liners, and other tubulars for oilfield operations as is understood in the art.
U.S. Pat. No. 6,138,774 proposes a pressure housing assembly containing a RCD and an adjustable constant pressure regulator positioned at the sea floor over the well head for drilling at least the initial portion of the well with only sea water, and without a marine riser. As best shown in FIG. 6 of the '774 patent, the proposed pressure housing assembly has a lubrication unit for lubricating the RCD. The proposed lubrication unit has a lubricant chamber, separated from the borehole pressure chamber, having a spring activated piston, or alternatively, the spring side of the piston is proposed to be vented to sea water pressure. The adjustable constant pressure regulator is preferably pre-set on the drilling rig (Col. 6, lns. 35-59), and allows the sea water circulated down the drill string and up the annulus to be discharged at the sea floor.
U.S. Pat. No. 6,913,092 B2 proposes a seal housing containing a RCD positioned above sea level on the upper section of a marine riser to facilitate a mechanically controlled pressurized system that is useful in underbalanced sub sea drilling. The exposed RCD is not enclosed in any containment member, such as a riser, and as such is open to atmospheric pressure. An internal running tool is proposed for positioning the RCD seal housing onto the riser and facilitating its attachment thereto. A remote controlled external disconnect/connect clamp is proposed for hydraulically clamping the bearing and seal assembly of the RCD to the seal housing. As best shown in FIG. 3 of the '092 patent, in one embodiment, the seal housing of the RCD is proposed to contain two openings to respective T-connectors extending radially outward for the return pressurized drilling fluid flow, with one of the two openings closed by a rupture disc fabricated to rupture at a predetermined pressure less than the maximum allowable pressure capability of the marine riser. Both a remotely operable valve and a manual valve are proposed on each of the T-connectors. As proposed in FIG. 2 of the '092 patent, the riser slip joint is locked in place so that there is no relative vertical movement between the inner barrel and the outer barrel of the riser slip joint. After the seals in the riser slip joint are pressurized, this locked riser slip joint can hold up to 500 psi for most 21¼″ marine riser systems. 
It has also become known to use a dual density fluid system to control formations exposed in the open borehole. See Feasibility Study of a Dual Density Mud System For Deepwater Drilling Operations by Clovis A. Lopes and Adam T. Bourgoyne, Jr., © 1997 Offshore Technology Conference. As a high density mud is circulated to the rig, gas is proposed in the 1997 paper to be injected into the mud column in the riser at or near the ocean floor to lower the mud density. However, hydrostatic control of formation pressure is proposed to be maintained by a weighted mud system, that is not gas-cut, below the seafloor.
U.S. Pat. No. 6,470,975 B1 proposes positioning an internal housing member connected to a RCD below sea level with a marine riser with an annular type blowout preventer (“BOP”) with a marine diverter, an example of which is shown in the above discussed U.S. Pat. No. 4,626,135. The internal housing member is proposed to be held at the desired position by closing the annular seal of the BOP on it so that a seal is provided in the annular space between the internal housing member and the inside diameter of the riser. The RCD can be used for underbalanced drilling, a dual density fluid system, or any other drilling technique that requires pressure containment. The internal housing member is proposed to be run down the riser by a standard drill collar or stabilizer.
U.S. Pat. No. 7,159,669 B2 proposes that the RCD held by an internal housing member be self-lubricating. The RCD proposed is similar to the Weatherford-Williams Model 7875 RCD available from Weatherford International, Inc. of Houston, Tex. Accumulators holding lubricant, such as oil, are proposed to be located near the bearings in the lower part of the RCD bearing assembly. As the bearing assembly is lowered deeper into the water, the pressure in the accumulators increase, and the lubricant is transferred from the accumulators through the bearings, and through a communication port into an annular chamber. As best shown in FIG. 35 of the '669 patent, lubricant behind an active seal in the annular chamber is forced back through the communication port into the bearings and finally into the accumulators, thereby providing self-lubrication. In another embodiment, it is proposed that hydraulic connections can be used remotely to provide increased pressure in the accumulators to move the lubricant. Recently, RCDs, such as proposed in U.S. Pat. Nos. 6,470,975 and 7,159,669, have been suggested to serve as a marine riser annulus barrier component of a floating rig's swab and surge pressure compensation system. These RCDs would address piston effects of the bottom hole assembly when the floating rig's heave compensator is inactive, such as when the bit is off bottom.
Pub. No. US 2006/0108119 A1 proposes a remotely actuated hydraulic piston latching assembly for latching and sealing a RCD with the upper section of a marine riser or a bell nipple positioned on the riser. As best shown in FIG. 2 of the '119 publication, a single latching assembly is proposed in which the latch assembly is fixedly attached to the riser or bell nipple to latch an RCD with the riser. As best shown in FIG. 3 of the '119 publication, a dual latching assembly is also proposed in which the latch assembly itself is latchable to the riser or bell nipple, using a hydraulic piston mechanism. A lower accumulator (FIG. 5) is proposed in the RCD, when hoses and lines cannot be used, to maintain hydraulic fluid pressure in the lower portion of the RCD bearing assembly. The accumulator allows the bearings to be self-lubricated. An additional accumulator (FIG. 4) in the upper portion of the bearing assembly of the RCD is also proposed for lubrication.
Pub. No. US 2006/0144622 A1 proposes a system and method for cooling a RCD while regulating the pressure on its upper radial seal. Gas, such as air, and liquid, such as oil, are alternatively proposed for use in a heat exchanger in the RCD. A hydraulic control is proposed to provide fluid to energize a bladder of an active seal to seal around a drilling string and to lubricate the bearings in the RCD.
U.S. Pat. Nos. 6,554,016 B1 and 6,749,172 B1 propose a rotary blowout preventer with a first and a second fluid lubricating, cooling, and filtering circuit separated by a seal. Adjustable orifices are proposed connected to the outlet of the first and second fluid circuits to control pressures within the circuits.
The above discussed U.S. Pat. Nos. 4,626,135; 5,662,181; 6,138,774; 6,470,975 B1; 6,554,016 B1; 6,749,172 B1; 6,913,092 B2; and 7,159,669 B2; and Pub. Nos. U.S. 2006/0108119 A1; and 2006/0144622 A1 are incorporated herein by reference for all purposes in their entirety. With the exception of the '135 patent, all of the above referenced patents and patent publications have been assigned to the assignee of the present invention. The '135 patent is assigned on its face to the Hydril Company of Houston, Tex.
Drilling rigs are usually equipped with drilling equipment for conventional hydrostatic pressure drilling. A need exists for a system and method to efficiently and safely convert the rigs to capability for managed pressure drilling or underbalanced drilling. The system should require minimal human intervention, particularly in the moon pool area of the rig, and provide an efficient and safe method for positioning and removing the equipment. The system should minimize or eliminate the need for high pressure slip joints in the marine riser. The system should be compatible with the common conventional drilling equipment found on typical rigs. The system should allow for compatibility with a variety of different types of RCDs. Preferably, the system and method should allow for the reduction of RCD maintenance and repairs by allowing for the efficient and safe lubrication and cooling of the RCDs while they are in operation.